Communication devices especially, but also other battery-powered devices, frequently include multiple lighting components in conjunction with visual displays and for other purposes. In the case of a portable telephone, for example, the telephone may include a main display and a keyboard backlight. In the case of a ‘clam shell’ type of telephone, where the main display is positioned inside a hinged cover that folds down over the keyboard when not in use, an auxiliary display of smaller size for displaying reduced information is often also provided on the outside of the cover.
The main and auxiliary displays typically comprise image displays, each of which defines an image in a layer for reflection and transmission of light. The image is visible by reflection of ambient light but a light emitting component is provided behind the image layer as a backlight to improve the image visibility by illuminating the image and transmission of light through the image layer. The image layer may comprise a liquid crystal display and the backlight may comprise a plurality of light emitting diodes (‘LED’s), for example. Such a configuration provides an effective display with low power consumption, particularly desirable in the case of battery powered portable devices.
The different lighting components are capable of being activated independently and each lighting component includes typically a plurality of light emitting elements in an array.
The quality of the lighting is judged by a number of criteria. Among the typical criteria are:                the uniformity of the lighting, especially within the main display, which requires all the lighting elements in the same array to be supplied with well-matched currents, but also between one lighting component and another,        low power consumption, which requires an efficient power supply, with a DC-DC converter, for example, and adapting the power supply voltage to reduce voltage drop in the drivers (‘headroom’ control), and        independent luminosity control for the different lighting arrays, which requires independent programming of the power supply currents for the different lighting arrays.        
Known lighting controller systems that address some or all of the above issues tend to suffer from some or all of the following drawbacks:                large semiconductor die area, especially if a parallel driver is used with an individual current source for each of the LEDs of the arrays in parallel,        high pin count of the integrated circuit, especially if individual current sources are provided for each LED in the lighting arrays,        limitation of the possible usage cases, especially if more than one lighting component cannot be active simultaneously or if the luminosity of different arrays is too different (the use of separate boost converters for different lighting arrays is excluded as requiring multiplication of costly self-inductances), and        limited efficiency, especially if the driver has no headroom control.        
The present invention has as objective to avoid or alleviate some or all of the above drawbacks while providing an improved quality of lighting.